Photographic color correction in imbibition printing



July l, 1958 E. A. WEAVER PHOTOGRAPHIC COLOR CORRECTION IN IMBIBITION PRINTING Filed March 2, 1953 nited States Patent PHOTOGRAPHIC COLOR CORRECTION IN IMBIBITION PRINTING Eastman A. Weaver, Winchester, Mass., assigner to Comstock & Wescott, Inc., Cambridge, Mass., a corporation of Massachusetts Application March 2, 1953, Serial No. 339,556

Claims. (Cl. 101-149.1)v

This invention deals with color photography and specifically with a new way of accomplishing `color-correction in prints made by dye-imbibition. A typical imbibition technique to which the present invention can be advantageously applied is described for instance in U. S. Patent 2,147,683.

It is known that coloring matters present in co-lor photo-A graphs, including dyes used for imbibition, undesirably absorb wavelengths they ought to transmit fully. The resulting pictures are consequently more or less dull and lackingin depth of color, especially if more than one set of imperfect dyes are involved, as when photographs are taken on `color lm and then prints are made by dye imbibition. In color-motion-pictures a third set of imperfections is introduced if the dupe negative from which prints are made is also a color lm, and this causes intolerable color-degradation in the absence of correction.

The methods for achieving such correction have generally involved photographic masking, i. e. the superposing in register of a positive component record with a negative of another component, and printing from this sandwich, as described in my U. S. Patent 2,183,598. Other schemes have been proposed, such as selective removal of part of the dye-content from one component matrix by imbibition into an undyed relief representing another component (U. S. Patent 2,600,75 6). Processing steps over and above those of simple imbibition, and involving increased expense are characteristic of such proposals.

One purpose of my invention is to diminish the amount of one component dye in an imbibition print proportionately to the amount of a second-component present, and in such proportion as to compensate for unwanted lightabsorption by the said second component.

Another purpose of my invention is to make color prints by simple imbibition, giving brighter and truer colors than have heretofore been obtainable by an inexpensive procedure.

Another purpose is to make unnecessary and to eliminate the masking processes noted above, and the other added steps and expedients which have served for colorcorrection.

Another purpose is to simplify the making of good color-motion pictures, making possible the use of color films as dupe negatives without undue color-degradation appearing in the prints.

The system according to my invention achieves these results by combining with one -of the imbibition `dye-baths a bleaching-agent which does notreact with that dye but which will bleach another of the dyes, namely the dye which properly absorbs wavelengths incorrectly absorbed by the rst named dye.

The process of my invention produces a color-corrected photograph which comprises in a colloid layer a plurality of coloring matters such as essentially yellow, magenta, and cyan dyes, and a colorless reaction-product of one of these, the concentration of the reaction product being a tricolor green iilter such as a Wratten B.

proportionate to the concentration of another coloring matter. In an embodiment which is particularly practical at this time, the colloid layer is mordanted and contains a cyan dye, a large-molecule sulfonated aldehyde, and a colorless reduction-product of a magenta dye, all three occurring in approximately proportional concentrations through the photograph; yellow dye of such photographs can be similarly corrected by reduction in proportion to the magenta dye concentration.

Other objects and aspects of novelty will appear-in addition to those contained in the above summary of the invention indicating its nature and substance including some of its objects-from the herein presented outline of its principles, its mode of operation and its practical possibilities together with a description of several typical embodiments illustrating its novel characteristics. These refer to drawings in which Fig. l is a ilow diagram illustrating the process according to the invention; and

Fig. 2 is a diagrammatical section through a print obtained according to the process of Fig. l.

The Worst defects in present-day imbibition dyes occur in the cyan component, which besides absorbing the red and orange light as intended, always absorbs a large proportion of green and a vconsiderable amount of blue light. I mix with this dye-bath a correct proportion of a bleaching agent inert to and compatible with the contained cyan dye but capable of bleaching the magenta dye component used. The bleaching agent should have a diffusion speed in the matrix not too diferent from that of the cyan dye, in order that washing or rinsing may affect both proportionately, and it should be of similar ionic character to the dye, i. e. if the latter is an acid dye, the bleach should be anionic also in order to avoid precipitation. Then when the dyes and blea-ch come together in the colloid layer, preferably mordanted, which is to form the print, the bleach reacts with part of the magenta dye, destroying an amount equivalent to the amount of bleach, which in turn is proportional to the amount of cyan dye, having been supplied by the same cyan-component matrix. Thus the amount Vof magneta destroyed is proportional throughout the picture to the amount of cyan dye present with its undesired green-light absorption, and if the relative strengths are correct, the bleaching otfsets the unwanted absorptivity and the requirement for color-correction is fulfilled. In a similar way, yellow dye can be destroyed in proportion to the amount of magenta to offset the latters unwanted blue-light absorption.

This bleaching action will ordinarily leave in the lm a harmless colorless reaction-product of the bleached dye which remains fixed on the mordant contained in the colloid layer. The concentration of this harmless reactionproduct, which is characteristic of and identifies one aspect of my invention, is approximately proportional to that of the dye, and also to that of the bleach-carrying agent, which is not destroyed in the process.

To determine the right proportion of bleach, no complicated measuring of densities and plotting of gradation scales are needed, as is usual with masking processes. Forexample, it is only necessary to make a uniformlydyed magenta area on the print paper, to imbibe on it the cyan-dye-b-leacn mixture from a matrix with a goed range of densities, and then to look at the result through if the proportion of bleach is right, the different areas all appear about equally dark, the green-absorption of the cyan dye being compensated by the bleaching of the magenta. If the deeper blue areas look denser through the green lter, the bleach is strengthened; if lighter, it is too strong and is weakened.

This procedure evaluates only the'degree lof correction needed by the imbibition dyes. In Acertain cases it is desirable to correct partially or wholly for other coloring matters such as those of the original taking film. In such cases, the above-described test shows the deeper blue areas appearing lighter through the green filter than the lighter blue areas, to a degree corresponding to the extra correction desired.

I found that members of one class of compounds are particularly suitable for purposes of the invention. These have a bleaching radical and an acid radical in common and comprise such a variety of possible molecular sizes and structures as sumces to afford a wide range of iinbibition speeds or mobilities. This class comprises the bisulfite addition products of the aldehyde and some ketone compounds of organic acids, particularly of the sulfonic acids. The methyl-ketone compounds are particularly successful.

The magenta dye -l have found to work best with these bleaches is Acid Fuchsin or Acid 'Magenta O, Colour Index #692. Many cyan dyes are available which the above bisulfite addition-compounds do not bleach; the one I prefer is Patent Blue V, Colour Index #712. The bisulfite addition compound preferred in sodium bisulfite plus O-Benzaldehydesulfonic Acid. The latter is commercially obtainable only as the sodium salt, in a (50%) technical grade, which works well in a ratio of 4 to 6 grams to one gram of sodium bisulfite.

The formula used with best results thus far is:

- Pontacyl Brilliant Blue V g 0.8 Sodium bisulfite g 3.1 O-benzaldehydesulfonic acid sodium salt (50% tech.) g 12.4 Phosphoric acid (85% syrupy) cc-- 4 Water cc- 1000 It is relatively immaterial which dye is imbibed first, but since aerial oxidation can destroy the bleach I prefer to imbide the magenta dye first.

Generally the yellow dye is sufficiently perfect to require no correction to bc made for it; but magenta dyes absorb so much blue light that it is often desirable in the same way to diminish the yellow in proportion to the amount of magenta dye present.

In cases where it is undesirable or inconvenient to use a dye to which the bleach is inert and with which it can therefore be harmlessly mixed, it is possible to apply the bleach separately by another application of the appropriate matrix or of a duplicate made for the purpose.

For example, I can use sodium sulfoxylate or hydrosulfite, in the form of an addition product with the aforesaid benZaldehyde-sulfonic acid, and imbibe it from the magenta matrix after having first imbibed the yellow dye from its matrix.

The above described technique is preferably carried out in the steps indicated in l as follows.

A blank film P is provided, preferably comprising a mordanted hydrophylic colloid layer E (Fig. 2) on a conventional transparent or opaque support S, for receiving three color aspect records from three gelatin relief matrices Y, M, C, in minus blue (yellow), minus green (magenta) and minus red (cyan) imbibition dyes,.repre sentingthe blue, green and red color aspects respectively. The matrices can be of the conventional overall relief wash-oit type, or they can be half tone dot reliefs permitting contrast control by flashing and otherwise. A cyan dye is applied to matrix C, for example as described in my above-mentioned patent, and this dye contains admixed thereto a bleaching agent which is compatible with the cyan dye but capable of destroying the magenta dye used for the particular printing. This magenta dye is applied to matrix M.

Matrix M is brought into contact with blank P, as for example described in my above patent andthe blank, now designated Pi, receives a magenta'record `of the green color aspect. Matrix C is next brought into contact `with P1.

Uponcontact `of .C with P1 (remembering `that-C contains a record of the red color aspect in terms of a bleach for the magenta dye), the magenta record of the green color aspect is reduced by the bleach of C, pictorially corresponding to the red aspect record of C. In other words the red and green aspect records of blank P2 are now mutually compensated, that much of the magenta dye having been destroyed as corresponds tothe undesired green absorption of the cyan dye.

The third record is then printed in yellow dye on blank P2 carrying the compensated magenta and .cyan pictures, resulting in the final print P3.

As indicated in Fig. 2, the intermediate stage P2 `as well as the final print P3 contain dyes as Well as a colorless reaction product of a dye and the bleach, and the bleach-carrier if used.

It should be understood that the present disclosure is for the purpose of illustration only and that4 this invention includes all modificationsand equivalents which .fall within the scope of .the appended claims.

I claim:

l. A method of producing color-corrected imbibition prints comprising the steps of mixing in solution a printing dye having undesired spectral absorption with a bleaching agent that is inert to said dye but capable of bleaching a second printing dye, and of printing one color aspect record with the mixture and another color-aspect record with the second dye, whereby the bleaching agent reduces the second dye to correct for undesirable absorption of the first dye in a spectral region properly absorbed by the second dye.

2. Method according to claim l wherein said bleaching agent comprises an addition product of a reactive component and a sulfonic acid of high molecular weight.

3. Method according to claim 1 wherein said printing dye is acidic and said bleaching agent is acidic in character and has similar speed of diffusion to that of said acidic dye with which it is mixed.

4. A method of producing color-corrected imbibition transfer prints comprising local bleaching of one dye-component in amounts proportioned to the amount of a second dye-component which has undesired spectral absorption which is compensated by said bleaching.

5. A process for color correction of imbibition color prints comprising the reacting of a bleaching agent imbibed from a relief matrix representing one color-component of a picture with the coloring material representing another component, thereby decolorizing said coloring material to an extent proportionate to the values of said first-mentioned component.

6. Process according to claim 5I wherein the bleachfis mixed with coloring material representing said first-mentioned color component.

7. Process according to claim 5 wherein the bleaching agent is an addition-compound of a small-molecule bleaching agent and a large-molecule auxiliary which serves to regulate the speed with which the addition prod.

uct imbibes and washes out.

8. Process according to claim 7 wherein the bleaching agent is a sulfnrous compound and the auxiliary has acid properties.

9. Process according to claim 7 wherein the auxiliary is a sulfonate.

l0. Process according to claim 7 wherein the auxiliary is a sulfonated aldehyde.

ll. Process according to claim 7 wherein the auxiliary is a sulfonated methyl-ketone.

l2. Process according to claim 7 wherein the auxiliary is an organic acid capable of forming a reactive additioncompound with said bleaching compound.

13. A color-corrected photograph comprising in a single colloid layer a plurality of dyes and a colorless reaction-product of one of said dyes, the concentration of said colorless reaction-product being proportionate to the concentration lof another one of said dyes.

14. A color-corrected photograph comprising in a mordantedfcolloid layer a cyan dye, a large-molecule sulfonated aldehyde, and a colorless reduction product of a magenta dye, al1 three being present in approximately proportional concentrations thorughout the photograph.

15. A color-corrected photograph comprising in a mordanted colloid layer a magenta dye, a large-molecule sulfonated aldehyde, and a colorless reduction product of a yellow dye, the magenta dye, the reduction product, `and the aldehyde being present in approximately proportional concentrations throughout the photograph.

References Cited in the le of this patent UNITED STATES PATENTS 6 Albrecht et a1. Aug. 30, 1938 Dyer Nov. 7, 1939 Gaspar Dec. 12, 1939 Becherer May 7, 1940 Martin et a1 Dec. 3, 1940 Land July 14, 1942 Weyerts Feb. 8, 1944 Weyerts Jan. 9, 1951 Gresham June 17, 1952 Conda Sept. 15, 1953 FOREIGN PATENTS Great Britain Oct. 30, 1930 OTHER REFERENCES 

1. A METHOD OF PRODUCING COLOR-CORRECTED IMBIBITION PRINTS COMPRISING THE STEPS OF MIXING IN SOLUTION A PRINTING DYE HAVING UNDESIRED SPECIAL ABSORPTION WITH A BLEACHING AGENT THAT IS INERT TO SAID DYE BUT CAPABLE OF BLEACHING A SECOND PRINTING DYE, AND OF PRINTING ONE COLOR ASPECT RECORD WITH THE MIXTURE AND ANOTHER COLOR-ASPECT RECORD WITH THE SECOND DYE, WHEREBY THE BLEACHING AGENT REDUCES THE SECOND DYE TO CORRECT FOR UNDESIRABLE ABSORPTION OF THE FIRST DYE IN A SPECTRAL REGION PROPERLY ABSORBED BY THE SECOND DYE. 